Field splice assembly for tactical fiber optic cable

ABSTRACT

An optical fiber connector assembly and method for splicing a broken fiber optic cable is described which includes first and second elements joinable in a mated condition along respective first and second mating surfaces; first and second grooves in the mating surfaces extending essentially the lengths of the surfaces and defining a channel of preselected size through the assembly in the mated condition for receiving the cable sheath within the assembly in the mated condition; a cavity in one of the mating surfaces for receiving the abutting optical fiber ends; an adhesive for holding the optical fiber ends in abutting relationship; an ambient temperature curing material sealing the mating surfaces from moisture and foreign substances and fixing the abutting optical fiber ends within the assembly; and a plurality of screws for assembling the elements.

RIGHTS OF THE GOVERNMENT

The invention described herein may be manufactured and used by or forthe Government of the United States for all governmental purposeswithout the payment of any royalty.

BACKGROUND OF THE INVENTION

The present invention relates generally to connectors for opticalfibers, and more particularly to a splice assembly for a broken opticalfiber cable.

Optical fibers have found substantial use as optical data links incommunications systems. Accompanying this use have arisen in themaintenance and repair of fiber optic systems reguirements for devicesand methods for rapid, efficient and effective splicing of opticalfibers. Consequently, development of fiber optic splices characterizedby low optical transmission losses has received substantial attention inthe telecommunications industry. Two basic methods for making opticalfiber splices have been developed, viz. fusion splicing and mechanicalsplicing. Fusion splicing involves the exact positioning and meltingtogether of two abutting fiber ends, usually by an electric arc. Infusion splicing of optical fibers within current technology, precisepositioning apparatus and relatively large and bulky equipment arerequired to make splices having low transmission losses of the order of0.05 dB or less. Mechanical splices, in which the fibers are joined(butted) together but are not melted or fused together, are generallyeasier to make but usually have optical transmission losses higher thanthat of fusion splices. In making a mechanical splice, strain relief forthe abutting fibers must be provided to keep the relatively fragileglass fibers from being broken by further handling. An enclosure for thesplice is usually included in the connecting assembly for retaining thesheathing of the cable in order to accommodate loads which may be placedon the cable.

Tactical fiber optic cable is designed for rugged physical environments.such as vehicle roll-overs and temperature extremes, to which normaltelecommunications grade fiber optic cable is not exposed. If a tacticalfiber optic cable is damaged in a military environment, it must bespliced quickly and effectively. Ideally, such a splice has low opticaltransmission loss, is easy to make, and does not require special toolsor extensive operator training.

Current practice for field repair of two-fiber tactical fiber opticalcable includes use of a splice kit comprising a splicing machine andvarious hand tools required for construction of the splice, all carriedwithin a 17×18×15 inch container and weighing about 25 pounds. Thesplice assembly made using the kit includes a 1.25×1×10 inch housing andstrain relief for the splice requires fastening the synthetic fiberstrength members within crimped sleeves. The kit is cumbersome andexpensive and requires special tools, precision use and specializedtraining of operators.

The present invention provides assembly and method for splicing a brokenfiber optic cable under severe field service conditions withoutexpensive complicated or heavy tools or equipment. Splicing opticalfibers according to the invention is performed by cutting away portionsof the cable to expose the broken ends of the optical fibers, cleavingthe fiber ends and adhesively fixing the ends in abutting relationshipwithin elastomeric, tubular splice assemblies, and fixing the spliceassemblies within plastic or epoxy material in a two-part protectivehousing. The splice may be made by a minimally trained operator in 15minutes or less, and is usually characterized by a transmission loss of0.5 dB or less.

It is therefore a principal object of the invention to provide aconnector structure for splicing a broken optical fiber.

It is a further object of the invention to provide a rugged, inexpensiveand easily assembled splice for field repair of a fiber optic cable.

It is yet another object of the invention to provide a simple andeffective method for rapid repair of fiber optic cables.

These and other objects of the invention will become apparent as thedetailed description of representative embodiments proceeds.

SUMMARY OF THE INVENTION

In accordance with the foregoing principles and objects of theinvention, an optical fiber connector assembly and method for splicing abroken fiber optic cable is described which includes first and secondelements joinable in a mated condition along respective first and secondmating surfaces; first and second grooves in the mating surfacesextending essentially the lengths of the surfaces and defining a channelof preselected size through the assembly in the mated condition forreceiving the cable sheath within the assembly in the mated condition; acavity in one of the mating surfaces for receiving the abutting opticalfiber ends; an adhesive for holding the optical fiber ends in abuttingrelationship; an ambient temperature curing material sealing the matingsurfaces from moisture and foreign substances and fixing the abuttingoptical fiber ends within the assembly; and a plurality of screws forassembling the elements.

DESCRIPTION OF THE DRAWINGS

The invention will be clearly understood from the following detaileddescription of representative embodiments thereof read in conjunctionwith the accompanying drawings wherein:

FIG. 1 is an exploded isometric view of a splice assembly housingstructure of the invention; and

FIG. 2 is a plan view of a fiber optic cable splice assembly structureof the invention.

DETAILED DESCRIPTION

Referring now to FIG. 1, shown therein is an exploded isometric view ofa field splice housing assembly 10 structure of the invention. In thepreferred configuration depicted in FIG. 1, assembly 10 comprises a pairof substantially rectangularly shaped portions 11,12 presentingrespective confronting and mating surfaces 13,14. Surfaces 13,14 havedefined therein respective longitudinal grooves 15,16 extendinglengthwise of the respective portions 11,12. Grooves 15,16 areconfigured to register with each other in the assembled condition todefine a channel for receiving and holding the fiber optic cable sheathas described below. Grooves 15,16 therefore preferably include aplurality of annular or longitudinal striations 17,18 providing grippingsurfaces for the cable sheath. Portions 11,12 may be constructed of anysuitable material and by any suitable process as would occur to oneskilled in the appropriate art, the same not being limiting of thisinvention. Accordingly, aluminum, plastic, epoxy, fiber glass, nylon, orother structural material may be selected, and portions 11,12 may becast, injection molded or otherwise formed depending on the materialselected. Weight restrictions on assembly 10 may dictate selection of alightweight material. One representative fabrication method for portions11,12 comprises selecting a piece of stock of the selected materialhaving size corresponding to the desired overall length and crosssection of the completed assembly 10 structure. The overall size ofassembly 10 may be selected over a wide range, and may be small tofacilitate winding of a spliced cable on a reel. The piece of stock isdrilled lengthwise to a bore size corresponding to the intended channeldiameter for accommodating the cable to be spliced. The resultingdrilled hole is tapped or otherwise scored to provide striations 17,18,and the piece of stock is then cut lengthwise along the axis of thedrilled hole to provide portions 11,12. In an assembly 10 built indemonstration of the invention a piece of one-inch square aluminum barstock about seven inches long was drilled lengthwise to about 0.219 inchdiameter (about 0.1 inch smaller than the diameter of the cable sheathto be clamped), and cut to provide the representative configuration forportions 11,12 shown in FIG. 1. Portions 11,12 are illustrated in FIG. 1as each having a rectangular cross section, but may be fabricated fromstock in other shapes (e.g., round stock), of any preselected lengthconsistent with space availability for the cable splice.

A plurality of holes 21 are drilled through portion 12 in registrationwith a corresponding plurality of tapped holes 22 in portion 11 forreceiving screws 23 (eight in the demonstration unit) for assembly ofportions 11,12. Screws 23 may be held captive in portion 11 forconvenience and to avoid loss of one or more of them. Confrontingshoulders 25,26 may be machined in portions 11,12 substantially as shownto provide a groove to receive excess sealing material in the assemblyof the portions 11,12 described below. Drilling and tapping of holes21,22 may be performed in the piece of stock prior to the lengthwise cutjust mentioned to ensure precision alignability of portions 11,12.Further, grooves of appropriate size may be machined on correspondingopposite sides of the piece of stock which following the lengthwise cut,define shoulders 25,26. Use of nylon screws 23 with plastic, epoxy ornylon structural material for portions 11,12 provides an all-dielectricassembly housing having no metallic components.

A cavity 29 of appropriate preselected size is machined or otherwiseformed into one of portions 11,12, substantially as shown in FIG. 1, toreceive the optical fiber ends to be spliced. In the demonstraton unit,cavity 29 was about three inches long by 0.75 inch wide by 0.30 inchdeep. Cavity 29 may be tapered at ramps 30 to facilitate placement offiber ends therein as described below and to eliminate sharp edges whichmight otherwise cut into a spliced fiber in the assembly.

Referring now additionally to FIG. 2, shown therein is a plan view of afiber splice assembly according to the invention with (top) portion 12removed. The damaged portion of a fiber optic cable 33 is cut away anddiscarded, which results in cable ends 34,35 to be spliced. Thesheathing of each end 34,35 is stripped back a preselected length (abouttwo inches), and the synthetic fiber strands and other tensile strengthmembers are cut away to expose the plurality of optical fibers 37 withincable 33. Any plurality of fibers 37 (about 0.0087 to 0.035 inchdiameter) may be included in cable 33, and the two fibers shown in FIG.2 are only representative of that plurality. The buffering (plasticlike)compound layer 39 on each fiber is stripped off, leaving about 0.75 inchof buffering layer 39 between respective fibers 37 and the sheathing ofcable ends 34,35. Fibers 37 are cleaved with a carbide tipped cleavingpen or other sharp blade a preselected length (about 1/2 inch) from thebuffering. Various appropriate lengths for stripping sheathing fromcable 33 and buffering layer 39 from fibers 37 and for cleaving fibers37 in assembling the splice may be indicated on a gauge scribed on theunderside of portion 11 as a convenient guide to an operator performinga splice, as this may vary according to the exact type of splicingmethod chosen. Corresponding fiber 37 ends are then joined in abuttingrelationship within an elastomeric sheath 41 of inner diametercorresponding to that of fibers 37 and about one inch long, and anappropriate epoxy or other adhesive is applied to fibers 37 at the endsof the elastomeric sheath to hold the fiber ends in abuttingrelationship. Other readily available splicing techniques may be used inplace of the elastomeric sheath, such as bent rod, V-groove or rotarytermini splices, providing the splice used may be contained with cavity29. Cable 33 with corresponding fiber 37 ends joined as just describedis then inserted into portion 11 with the spliced fiber 37 joints lyingwithin cavity 29.

A gasket forming or similar ambient (or room temperature) curing sealingmaterial 43 is poured into or otherwise liberally applied to cavity 29and the mating surfaces around cable 33 lying in groove 15 to fix thespliced fiber 37 joints in place. Material 43 may comprise any suitablesubstantially room temperature curing plastic, epoxy or elastomericmaterial such as silicone rubber sealant, RTV or automotive gasketcompound, as would occur to the skilled artisan guided by theseteachings. Material 43, when set, substantially fills cavity 29 andserves both to hold the fiber 37 ends in abutting relationship and toseal the splice against intrusion by water. Portion 12 is then mated toportion 11 and screws 23 tightened firmly to form assembly 10. Excessgasket material 43 is removed and, if desired, the entire assembly 10 iswrapped with electrical or other suitable tape for additionalprotection.

Tests conducted on the demonstration unit described above to determinelosses incurred by the compressive force of the splice assembly on thecable showed an average compressive loss of about 0.03 dB, Strain relieftests on the splice assembly to determine the force required to pull thecable ends from the assembly indicated that the assembly will stand aminimum of 200 pounds.

The invention therefore provides a novel splice assembly and method forconnecting broken optical fibers. Expensive special tools to perform asplice are not required, since only normal hand tools, such as a hexwrench, sharp blade and/or screwdriver, pliers or small wrench may beused. The clamping action of the assembly provides strain relief for thespliced cable. The assembly is inexpensive and splicing operation of theinvention may be performed by operators without specialized training.

It is understood that certain modifications to the invention may be madeas might occur to one with skill in the field of the invention withinthe scope of the appended claims. All embodiments contemplated hereunderwhich accomplish the objects of the invention have therefore not beenshown in complete detail. Other embodiments may be developed withoutdeparting from the spirit of the invention or from the scope of theappended claims.

I claim:
 1. An assembly for splicing abutting ends of an optical fiberof a fiber optic cable having a sheath enclosing at least one saidoptical fiber comprising:(a) first and second elements having respectivefirst and second mating surfaces, said first and second elements beingjoinable in a mated condition along said first and second matingsurfaces; (b) means defining first and second grooves in respective saidfirst and second mating surfaces, said first and second groovesextending lengthwise of said first and second mating surfaces anddisposed on respective said first and second elements in configuratingrelationship to each other in said mated condition whereby a channel isdefined through said assembly in said mated condition, said first andsecond grooves having preselected size corresponding to the size of saidsheath of said cable for holding said sheath within said assembly insaid mated condition; (c) means defining a cavity in one of said matingsurfaces for receiving the abutting ends of said optical fiber; (d)adhesive means for holding said abutting ends of said optical fiber inabutting relationship; (e) a plurality of striations on the surfacesdefining said grooves for gripping said sheath of said cable; and (f)means for joining said first and second mating elements in said matedcondition.
 2. The assembly of claim 1 further comprising ambienttemperature curing material within said cavity for holding said abuttingends of said optical fiber within said assembly.
 3. The assembly ofclaim 2 wherein said ambient temperature curing material is selectedfrom the group consisting of silicone rubber sealant, RTV, and gasketcompound.
 4. The assembly of claim 1 wherein said first and secondmating elements comprise a material selected from the group consistingof aluminum, plastic, epoxy, fiber glass, and nylon.
 5. The assembly ofclaim 1 wherein said means for joining said first and second matingelements in said mated condition comprises a plurality of screws.
 6. Theassembly of claim 1 wherein said adhesive means includes an elastomericsheath for receiving said abutting ends of said optical fiber and anadhesive at each end of said elastomeric sheath for holding saidabutting ends in abutting relationship.
 7. A method for splicingabutting ends of an optical fiber of a fiber optic cable having a sheathenclosing at least one said optical fiber comprising:(a) providing anassembly including:(i) first and second elements having respective firstand second mating surfaces, said first and second elements beingjoinable in a mated condition along said first and second matingsurfaces; (ii) means defining first and second grooves in respectivesaid first and second mating surfaces, said first and second groovesextending lengthwise of said first and second mating surfaces anddisposed on respective said first and second elements in confrontingrelationship to each other in said mated condition whereby a channel isdefined through said assembly in said mated condition, said first andsecond grooves having preselected size corresponding to the size of saidsheath of said cable and further including a plurality of striations onthe surfaces defining said grooves for holding said sheath within saidassembly in said mated condition; and (iii) means defining a cavity inone of said mating surfaces for receiving the abutting ends of saidoptical fiber; (b) adhesively joining said abutting ends of said opticalfiber in abutting relationship; (c) inserting the adhesively joined saidabutting ends of said optical fiber into said cavity with the sheath ofcorresponding ends of said cable lying within the groove of said one ofsaid first and second mating surfaces; (d) joining said first and secondmating elements in said mated condition with said cable generallybetween said elements.
 8. The method of claim 7 further comprising thestep of filling said cavity with ambient temperature curing material forholding said abutting ends of said optical fiber within said assembly.9. The method of claim 7 wherein said first and second mating elementscomprise a material selected from the group consisting of aluminum,plastic, epoxy, fiber glass, and nylon.
 10. The method of claim 7wherein said step of joining said first and second mating elements insaid mated condition with said cable generally between said elements isperformed utilizing a plurality of screws.
 11. The method of claim 8wherein said ambient temperature curing material is selected from thegroup consisting of silicone rubber sealant, RTV, and gasket compound.12. The method of claim 7 wherein said step of adhesively joining saidabutting ends of said optical fiber in abutting relationship isperformed utilizing an elastomeric sheath for receiving said abuttingends of said optical fiber and an adhesive at each end of saidelastomeric sheath for holding said abutting ends in abuttingrelationship.